In internal combustion engines with mechanical valve control, gas exchange valves are actuated by cams of a camshaft-driven camshaft, wherein the control times of the valves can be determined by the arrangement and shape of the cams. Changing the rotational angle position (phase position) between the crankshaft and camshaft can influence the control times of the valves, wherein advantageous effects, such as reducing fuel consumption and pollutant generation can be achieved. For a long time, the use of special devices has been known for adjusting the phase position between the crankshaft and camshaft, wherein these devices have usually been designated “camshaft adjusters.”
In general, camshaft adjusters comprise a drive part in drive connection with the crankshaft and a camshaft-fixed driven part, as well as an adjustment mechanism that is connected between the drive part and driven part for the transfer the torque from the drive part to the driven part and enables adjustment and fixing of the phase position between these two parts. In the case of a hydraulic adjustment mechanism, at least one pair of counteracting pressure chambers is provided between the drive part and driven part and this pair of chambers can be selectively charged with pressurized medium, in order to rotate the drive part and driven part relative to each other and to cause a change in the phase position between the crankshaft and camshaft. Hydraulic camshaft adjusters are described in detail, for example, in publications DE 202005008264 U1, EP 1596040 A2, DE 102005013141 A1, DE 19908934 A1, and WO 2006/039966 of the applicant.
Hydraulic adjustment mechanisms conventionally comprise an electronic control device that regulates the feed and discharge of pressurized medium by means of an electromagnetically activated control valve on the basis of the current operating state of the internal combustion engine. Typically, the control valves comprise a cylindrical valve housing and a control piston that can be displaced axially in the interior of the valve housing and can be displaced by an electromagnetically moveable push rod against the spring force of a restoring spring element. Such control valves are well known as such and are described in detail, for example, in the German Patent DE 19727180 C2, the German Patent DE 19616973 C2, and also the European Patent Application EP 1 596 041 A2 of the applicant.
In one common design, the driven part of the camshaft adjuster is provided with a central axial opening that is penetrated by a central screw that is screwed into an end-side threaded opening of the camshaft. The driven part and the camshaft are connected to each other in a non-positive manner (rotationally locked) by the central screw. Such a fastening of the camshaft adjuster on the camshaft is shown, for example, in the German Laid Open Patent Application DE 102004038681 A1.
As is known to someone skilled in the art, it is typical for hydraulic camshaft adjusters that the valve housing of the control valve also takes over the function of the central screw, so that the driven part is locked in rotation with the camshaft by the control valve.
From DE 19955507 C2, an alternative fastening of the camshaft adjuster by a central screw connection to the camshaft is further known in which a clamping nut is screwed on a screw shaft connected to the camshaft, wherein the driven part of the camshaft adjuster is clamped axially with a flange part of the screw shaft.